U.S. patent number 9,201,000 [Application Number 14/141,827] was granted by the patent office on 2015-12-01 for sensor apparatus and method based on wavelength centroid detection.
This patent grant is currently assigned to Palo Alto Research Center Incorporated. The grantee listed for this patent is Palo Alto Research Center Incorporated. Invention is credited to Peter Kiesel, Alexander Lochbaum, Ajay Raghavan, Bhaskar Saha, Lars Wilko Sommer, Tobias Staudt.
United States Patent |
9,201,000 |
Kiesel , et al. |
December 1, 2015 |
Sensor apparatus and method based on wavelength centroid
detection
Abstract
Sensor material is arranged to interact with input light and to
asymmetrically alter a spectral distribution of the input light in
response to presence of an external stimulus. A detector is
configured to sense the altered input light and to generate at
least one electrical signal comprising information about a shift in
the centroid of a spectral distribution of the altered input light
relative to a centroid of the spectral distribution of the input
light.
Inventors: |
Kiesel; Peter (Palo Alto,
CA), Lochbaum; Alexander (Moutain View, CA), Raghavan;
Ajay (Mountain View, CA), Saha; Bhaskar (Union City,
CA), Staudt; Tobias (Palo Alto, CA), Sommer; Lars
Wilko (Mountain View, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Palo Alto Research Center Incorporated |
Palo Alto |
CA |
US |
|
|
Assignee: |
Palo Alto Research Center
Incorporated (Palo Alto, CA)
|
Family
ID: |
52006937 |
Appl.
No.: |
14/141,827 |
Filed: |
December 27, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150185139 A1 |
Jul 2, 2015 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N
21/27 (20130101); G01N 21/77 (20130101); G01N
21/645 (20130101); G01N 21/78 (20130101); G01N
2201/062 (20130101); G01N 2201/0612 (20130101); G01N
2021/7783 (20130101); G01N 21/7703 (20130101); G01N
2021/7753 (20130101); G01N 2021/7786 (20130101); G01N
2021/7793 (20130101); G01N 2201/08 (20130101) |
Current International
Class: |
G01J
3/46 (20060101); G01N 21/27 (20060101); G01N
21/64 (20060101); G01N 21/77 (20060101); G01N
21/78 (20060101) |
Field of
Search: |
;356/300-445 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Gupta et al., "Evanescent Wave Absorption-Based Fiber Optic PH
Sensor Prepared by Dye Doped Sol-Gel Immobilization Technique".
Optics Communicatiions 4018 (97), pp. 30-33. cited by applicant
.
Ben-David et al., "Simple Absorption Optical Fiber PH Sensor Based
on Doped Sol-Gel Cladding Material", Chem. Mater., 1997, 9, pp.
2255-2257. cited by applicant .
Chan et al., "An Optical-Fiber-based Gas Sensor for Remote
Absorption Measurement of Low-Level CH4 Gas in the Near-Infrared
Region", Journal of Lightwave Technology, (3), 1984, pp. 234-237.
cited by applicant .
Sharma et al., Absorption-Based Fiber Optic Surface Plasmon
Resonance Sensor: A Theoretical Evalution, Chemical 100(3), 2004,
pp. 423-431. cited by applicant.
|
Primary Examiner: Nur; Abdullah
Attorney, Agent or Firm: Hollingsworth Davis, LLC
Government Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND
DEVELOPMENT
This invention was made with government support under contract
DE-AR0000274 awarded by ARPA-E (Advanced Research Projects
Agency-Energy). The government has certain rights in the invention.
Claims
What is claimed is:
1. A system, comprising: an analyte-specific sensor material
arranged to interact with input light and to asymmetrically alter a
spectral distribution of the input light in response to presence of
a specific analyte; and a detector configured to sense the altered
input light and to generate at least one electrical signal
comprising information about a shift in the centroid of a spectral
distribution of the altered input light relative to a centroid of
the spectral distribution of the input light in response to
presence of the specific analyte.
2. The system of claim 1, wherein the analyte-specific sensor
material has an absorption spectrum that is non-centered with
respect to an illumination spectrum of a light source that produces
the input light.
3. The system of claim 1, wherein the analyte-specific sensor
material has a fluorescence spectrum that is non-centered with
respect to an illumination spectrum of a light source that produces
the input light.
4. The system of claim 1, wherein the analyzer is configured to
determine a magnitude of the shift in the centroid of the altered
input light.
5. The system of claim 1, wherein the analyte-specific sensor
material is situated at the detector.
6. The system of claim 1, wherein: the input light is produced by a
light emitting device; and the analyte-specific sensor material is
situated at the light emitting device.
7. The system of claim 1, wherein: the input light is produced by a
light emitting device; an optical wave guide is disposed between
the light emitting device and the detector; and the
analyte-specific sensor material is situated on the optical wave
guide.
8. The system of claim 1, further comprising: a light emitting
device arranged to provide the input light; wherein the light
emitted by the light emitting device is spectrally shifted to
produce the input light.
9. The system of claim 1, further comprising: a light emitting
device arranged to provide the input light; wherein the light
emitted by the light emitting device is spectrally shifted by a
phosphor to produce the input light.
10. The system of claim 1, wherein: the analyte-specific sensor
material comprises an array of analyte-specific materials arranged
to interact with the input light, each of the analyte-specific
materials arranged to asymmetrically alter a spectral distribution
of the input light in response to presence of a specific analyte
associated with each of the analyte-specific materials; and the
detector is configured to determine shifts in each of the centroids
of the altered input light relative to a centroid of the spectral
distribution of the input light in response to presence of the
specific analytes.
11. The system of claim 10, further comprising an array of light
emitting devices, each light emitting device emitting light
associated with a particular analyte-specific material.
12. The system of claim 11, wherein the light emitted by each light
emitting device is spectrally shifted to produce the input light
for a particular analyte-specific sensor material.
13. A system, comprising: sensor material arranged to interact with
input light and to asymmetrically alter a spectral distribution of
the input light in response to presence of an external stimulus;
and a detector configured to sense the altered input light and to
generate at least one electrical signal comprising information
about a shift in the centroid of a spectral distribution of the
altered input light relative to a centroid of the spectral
distribution of the input light.
14. The system of claim 13, wherein the analyzer is configured to
determine a magnitude of the shift in the centroid of the altered
input light.
15. The system of claim 13, wherein the sensor material has an
absorption spectrum that is non-centered with respect to an
illumination spectrum of a light source that produces the input
light.
16. The system of claim 13, wherein the sensor material has a
fluorescence spectrum that is non-centered with respect to an
illumination spectrum of a light source that produces the input
light.
17. The system of claim 13, wherein the detector comprises a
position-dependent photo detection arrangement.
18. The system of claim 13, wherein the detector comprises a linear
variable filter and a split-diode detection arrangement.
19. A method, comprising: causing sensor material to interact with
input light, the sensor material asymmetrically altering a spectral
distribution of the input light in response to presence of an
external stimulus; sensing altered input light; and generating at
least one electrical signal comprising information about a shift in
the centroid of a spectral distribution of the altered input light
relative to a centroid of the spectral distribution of the input
light.
20. The method of claim 19, further comprising determining a
magnitude of the shift in the centroid of the altered input
light.
21. The method of claim 19, wherein the external stimulus comprises
an analyte.
22. The method of claim 19, wherein the external stimulus comprises
an electromagnetic field.
23. The method of claim 19, wherein the external stimulus comprises
a temperature.
24. The method of claim 19, wherein the external stimulus comprises
a gas concentration.
Description
TECHNICAL FIELD
This application relates generally to detection techniques for
sensing presence of an external stimulus. The application also
relates to components, devices, systems, and methods pertaining to
such techniques.
SUMMARY
Various embodiments of the application are directed to a system
which includes sensor material arranged to interact with input
light and to asymmetrically alter a spectral distribution of the
input light in response to presence of an external stimulus. A
detector is configured to sense the altered input light and to
generate at least one electrical signal comprising information
about a shift in the centroid of the spectral distribution of the
altered input light relative to a centroid of the spectral
distribution of the input light.
According to some embodiments, a system includes an
analyte-specific sensor material arranged to interact with input
light and to asymmetrically alter a spectral distribution of the
input light in response to presence of a specific analyte. A
detector is configured to sense the altered input light and to
generate at least one electrical signal comprising information
about a shift in the centroid of the spectral distribution of the
altered input light relative to a centroid of the spectral
distribution of the input light in response to presence of the
specific analyte.
Other embodiments are directed to a method involving causing sensor
material to interact with input light, such that the sensor
material asymmetrically alters a spectral distribution of the input
light in response to presence of an external stimulus. The method
also involves sensing altered input light and generating at least
one electrical signal comprising information about a shift in the
centroid of the spectral distribution of the altered input light
relative to a centroid of the spectral distribution of the input
light.
The above summary is not intended to describe each disclosed
embodiment or every implementation of the present disclosure. The
figures and the detailed description below more particularly
exemplify illustrative embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a general block diagram of a detection apparatus
according to embodiments described herein;
FIG. 2 illustrates a system for detecting presence of an external
stimulus using an optical-based detector in accordance with some
embodiments;
FIG. 3 illustrates a system for detecting presence of an external
stimulus using an optical-based detector in accordance with other
embodiments;
FIG. 4 illustrates a system for detecting presence of an external
stimulus using an optical-based detector in accordance with further
embodiments;
FIG. 5 shows the spectrum of a representative illuminating light
source in accordance with various embodiments;
FIG. 6 shows the absorption spectrum of a sensing layer arranged to
interact with input light in accordance with various
embodiments;
FIG. 7 shows a representative light source spectrum with a
representative absorption spectrum of a sensing layer in accordance
with various embodiments;
FIG. 8 shows a detector which includes a position sensitive device
and a filter that cooperate to convert wavelength information of
incident light into a spatial intensity distribution on the
detector in accordance with various embodiments;
FIGS. 9 and 10 show a readout apparatus in accordance with various
embodiments, and further shows a sensing layer of the apparatus
having an absorption spectrum which is incorporated completely into
one half of the illuminating spectrum of a light source (not to
scale) in accordance with various embodiments;
FIG. 11 shows a sensing scheme which includes a wavelength centroid
detector that uses only a certain portion of the light source
spectrum for determining changes to the centroid of the altered
light source spectrum in accordance with various embodiments;
FIG. 12 shows a sensing characteristic of an example sensing layer
and representative differential output signals of a wavelength
centroid detector in accordance with various embodiments;
FIG. 13 is a cross-sectional view of an integrated sensor structure
in accordance with various embodiments;
FIG. 14 shows a detection apparatus comprising an array of light
sources, an array of detectors, and an array of sensing layers
positioned therebetween in accordance with various embodiments;
FIG. 15 shows a detection apparatus comprising an array of light
sources, an array of phosphors of differing types, an array of
detectors, and an array of sensing layers of varying types
positioned therebetween.
FIG. 16 shows a light source spectrum with an analyte-induced
absorption dip and an analyte-induced change in the fluorescence
intensity in accordance with various embodiments;
FIG. 17 illustrates a detection apparatus comprising an array of
detectors, an array of phosphors of differing type, and an array of
sensing layers of varying type positioned between the array of
detectors and the array of phosphors in accordance with various
embodiments; and
FIG. 18 is a block diagram of a detection apparatus in accordance
with various embodiments.
The figures are not necessarily to scale unless otherwise
indicated. Like numbers used in the figures refer to like
components. However, it will be understood that the use of a number
to refer to a component in a given figure is not intended to limit
the component in another figure labeled with the same number.
DESCRIPTION
In the following description, reference is made to the accompanying
set of drawings that form a part of the description hereof and in
which are shown by way of illustration several specific
embodiments. It is to be understood that other embodiments are
contemplated and may be made without departing from the scope of
the present disclosure. The following detailed description,
therefore, is not to be taken in a limiting sense.
Unless otherwise indicated, all numbers expressing feature sizes,
amounts, and physical properties used in the specification and
claims are to be understood as being modified in all instances by
the term "about." Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the foregoing specification
and attached claims are approximations that can vary depending upon
the desired properties sought to be obtained by those skilled in
the art utilizing the teachings disclosed herein. The use of
numerical ranges by endpoints includes all numbers within that
range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and
any range within that range.
FIG. 1 is a block diagram of a system for detecting presence an
external stimulus using an optical-based detector in accordance
with various embodiments. The system shown in FIG. 1 includes
sensor material 104 arranged to interact with input light, such as
input light generated by a light source 102 or the sun, for
example. The sensor material 104 is designed to asymmetrically
alter a spectral distribution of the input light in response to
presence of an external stimulus 106. The system shown in FIG. 1
further includes a detector 108 configured to sense the altered
input light and to generate at least one electrical signal
comprising information about a location of a centroid of a spectral
distribution of the altered input light. The detector 108 is
configured to directly measure a shift in the centroid of the
altered input light relative to a centroid of the spectral
distribution of the input light rather than determining the
spectral distribution itself. The detector 108 may further be
configured to determine the magnitude or concentration of the
external stimulus sensed by the sensor material 104.
According to some embodiments, the sensor material 104 comprises
analyte-specific sensor material. In the presence of a specific
analyte, an optical property of the analyte-specific sensor
material 104 changes in a specified spectral range of the input
light spectrum. Representative optical properties of the
analyte-specific sensor material 104 that can change in the
presence of a specified analyte include absorption, transmission,
scattering, light emission or reflection in the specified spectral
range. A change of the optical property of the analyte-specific
sensor material due to presence of the specific analyte
asymmetrically alters the spectral distribution of the input light.
The detector 108 is configured to determine a shift in the centroid
of the altered input light relative to a centroid of the spectral
distribution of the input light in response to presence of the
specific analyte sensed by the sensor material 104. The detector
108 can also determine the magnitude or concentration of the
analyte sensed by the sensor material 104. For example, the shift
of the centroid of the spectral distribution of the input light is
related to the change in analyte concentration or the change in
magnitude of another form of external stimulus. After calibration
and/or referencing, such as to a detector without a sensing layer,
the detector 108 can directly measure the analyte concentration or
stimulus amplitude. The detector 108 or an analyzer coupled to the
detector 108 can include a display, which can indicate the presence
of an analyte(s) or other external stimulus (or stimuli) when
present, and may further display the analyte concentration or
stimulus amplitude, in textual and/or graphical form.
In accordance with other embodiments, the sensor material 104 is
arranged to interact with input light and asymmetrically alters a
spectral distribution of the input light in response to presence of
a specific electromagnetic field. In such embodiments, the sensor
material 104 can include ferrofluids (e.g., Fe.sub.2O.sub.3 in
octane), and measurements of filter characteristics for magnetic
fields between 110 G and 280 G (11 mT-28 mT) can be conducted. In
other embodiments, the sensor material 104 is arranged to interact
with input light and asymmetrically alters a spectral distribution
of the input light in response to presence of a specific
temperature or temperature range (thermochromism). In such
embodiments, the sensor material 104 can include
bis(diethylammonium)tetrachlorocuprate, and the specific phase
transition point is at 52-53.degree. C., evidence by a color change
from green to yellow in this illustrative example. According to
further embodiments, the sensor material 104 is arranged to
interact with input light and asymmetrically alters a spectral
distribution of the input light in response to presence of a
specific gas concentration or gas concentration range. In such
embodiments, the sensor material 104 can include Binuclear Rhodium
Complexes for CO detection or Bromocresol purple for NH.sub.3
detection, and the specific gas concentration can be defined in the
100 ppm range for CO and 5-1000 ppm for NH.sub.3, for example. The
section above describes specific examples; in more general terms,
the sensing layer 104 can interact and react to a large variety of
external stimuli including pressure, acoustic wave; static magnetic
or electric fields, and nuclear radiation, among others.
FIG. 2 illustrates a system for detecting presence of an external
stimulus using an optical-based detector in accordance with various
embodiments. In the embodiment shown in FIG. 2, the system includes
a light source 202 and a detector 204 spaced away from the light
source 202. The light source 202 can include a light emitting
device, such as a light emitting diode (LED), a laser diode or a
semiconductor laser, for example. An optical wave guide (e.g.
optical fiber) 206 is disposed between the light source 202 and the
detector 204. Sensor material 208 is situated in the optical wave
guide 206 to interact with the guided light. In the case of an
optical fiber, the whole or a part of the cladding material can be
replaced by the analyte/stimulus specific sensing material.
In general, the light source 202 should be a broad band light
source so that the sensing layer 208 can asymmetrically alter the
spectrum. Laser sources emitting a plurality of laser modes can
also be used. In the case of inelastic scattering (Raman
scattering), the spectral range impacted by the sensing layer 208
can be quite narrow and, therefore, so can that of the spectral
distribution of the light source (e.g., laser). As a general rule
for a sensitive system, the spectral distribution of the input
light should be about twice as broad as the affected spectral range
of the sensing layer 208. In this case, the sensing layer 208 can
most effectively asymmetrically modify the spectral distribution of
the input light.
In the embodiment illustrated in FIG. 3, the system includes a
light source 302 spaced apart from a detector 304. In the
embodiment of FIG. 3, sensor material 308 is situated at the light
source 302, and can completely cover the light source 302 for
enhanced sensitivity. For example, the sensor material 308 can be
deposited on or be in contact with the light source 302. In the
representative embodiment shown in FIG. 4, the system includes a
light source 402 and a detector 404 spaced away from the light
source 402. According to this embodiment, sensor material 408 is
situated at the detector 404, and can completely cover the detector
404 for enhanced sensitivity. The sensor material 408, for example,
can be deposited on or be in contact with the detector 404.
Optional optics 410 may be included within the system shown in FIG.
4 (or that shown in FIG. 3), such as between the light source 402
and the sensor material 408. In the embodiments illustrated in
FIGS. 2-4, the sensor material 208, 308, 408 is arranged to
interact with input light produced by the light source 202, 302,
402, respectively, and to asymmetrically alter a spectral
distribution of the input light in response to presence of an
external stimulus, which may be sensed within a detection region or
volume 206, 305, 405.
Referring again to the embodiment illustrated in FIG. 2, the system
can include an LED as a light source 202 coupled into an optical
wave guide 206 which is coated with an analyte-specific coating 208
(a representative example of sensor material or a sensing layer).
The sensing layer 208 has one or more optical properties that
change in the presence of a specific analyte. The input light
produced by the LED is preferably broad band light with a certain
center wavelength and FWHM (Full-Width Half-Maximum). The presence
of an analyte changes the transmission properties of the
analyte-specific coating 208 on the optical wave guide 206 in a
certain spectral range. Depending on the nature of the sensing
layer 208, the presence of the analyte can either increase or
decrease the absorption in this spectral range according to some
embodiments. The sensing layer spectrum and LED spectrum are chosen
so that the presence of an analyte causes a change in the spectral
distribution (e.g., centroid of the spectral distribution) of the
LED spectrum. In some embodiments, a wavelength centroid detector
204 is configured to measure a wavelength shift of the centroid of
the spectral distribution of the altered input light (the
analyte-induced changes of the LED spectrum) and to measure the
analyte concentration.
According to various embodiments, the presence of an analyte causes
a change in the transmitted, scattered, emitted (fluorescence) or
reflected intensity of the sensing layer 208 in a certain spectral
range. A change in the intensity of the sensing layer 208 impacts
the spectral distribution of the incident (broad band) light source
202. The analyte concentration can be deduced from changes of a
centroid of the spectral distribution (e.g., color change) of the
altered input light. The center wavelength of the input light
(e.g., filtered white light, LED or RC LED, broad band or multiple
wavelength emission laser) and the center wavelength of the
analyte-induced intensity change should not be centered. In some
embodiments, a greater change in the centroid of the input light
can be achieved if the analyte affects only one half of the
incoming light spectrum. According to such embodiments, the sensing
layer 208 is arranged to asymmetrically alter a spectral
distribution of the input light in response to presence of a
specific analyte, such that only one half of input light spectrum
is affected by presence of the analyte.
Provided herein are several representative implementations of fiber
based systems, such as systems with a coated LED or LED array. It
is understood that the principles disclosed herein can be employed
in many other analogous or similar implementations. Many of the
representative examples provided herein use sensing layers which
modify the centroid of the incoming light spectrum by creating
absorption dips in the transmitted or reflected spectrum. It is
understood that a sensing layer that provides for analyte-induced
changes in other optical properties (elastic or inelastic light
scattering, reflection, fluorescence emission, etc.) can be used to
modify the spectral distribution of the incoming light. Embodiments
of the disclosure provide for measuring a shift of the wavelength
distribution of altered input light rather than determining the
intensity at a certain wavelength (band), which is elegant and
relatively simple since it does not require any wavelength
referencing, thus enabling the implementation of very low cost
systems.
The readout of intensity-encoded sensors, both fiber-based sensors
and non-fiber-based sensors, is typically accomplished by intensity
measurements, either via analyzing the optical spectrum at a
certain wavelength or by illumination with a light source of
certain spectral range (which spectrally overlaps with the
absorption spectrum of sensing layer) and measurement of the
intensity of the light after interaction with the sensing later is
recorded. In order to increase sensitivity, often a second
wavelength which does not spectrally overlap with the absorption
spectrum is measured for reference. Examples for absorption-based
fiber sensors are evanescent wave absorption-based fiber sensors.
The evanescent field of the guided light in the fiber overlaps with
the sensing agent directly or with a transducing material (e.g.,
coating, in cladding incorporated dye, etc., in general called
"sensing material" in the following discussion). The propagation of
the evanescent light wave through this region is connected with
higher losses compared to the fiber core. Furthermore, the losses
sensed by the evanescent field alter with the concentration of
agent to be sensed. Hence, the intensity of the transmitted light
through the fiber depends on the agent concentration.
Optical absorption-based sensors are also used in the form of
non-fiber-based solutions. Excitation and detection in the infrared
regime is, for example, currently used in conventional smoke
detectors. Here, the intensity measurement is referenced against
its own dark spectrum, i.e. if the illuminating diode is turned off
in order to enable a coarse threshold measurement. To make the
measurements independent of fluctuations of the light source and
other distortions in the intensity of the signal, the measured
intensity in the absorption band of the sensor (e.g., 570-580 nm)
must be set into relation to the intensity of a band outside of the
absorption range of the sensor (e.g., 910-920 nm), which spectrum
is not altered by absorption of the sensing material. Thus,
intensity measurements are based on the calculation of a relative
intensity at two different wavelengths, respectively wavelength
bands (or in other words, of an intensity ratio). Such readout
schemes require either an expensive readout unit (e.g., optical
spectrum analyzer) or multiple light sources and detectors (e.g.,
LEDs and photodiodes), which increase both complexity and cost of a
readout system.
Embodiments of the present disclosure provide a readout scheme that
does not depend on the evaluation of different intensities (e.g.,
intensity ratio) as described above, but instead detects a change
in the spectral distribution of the input light due to the optical
response of the sensing layer to the presence of a certain external
stimulus, such as a specific analyte. Thus, there is no need to
reference the measurement against another wavelength band, which
makes both a second detector and a second light source obsolete.
According to various embodiments, the detection methodology
disclosed herein exploits the fact that the centroid of the
absorption spectrum of the sensing layer is different when compared
to the centroid of the input light source. In other words, the
absorption spectrum of the sensing layer is placed non-centered in
the illumination spectrum of the light source and thus sees a
monotonic baseline.
By way of example, FIG. 5 shows the spectrum of a representative
illuminating light source, such as the light source illustrated in
FIGS. 1-4. The illuminating light source of FIG. 5 may be a
(spectrally filtered) tungsten-halogen bulb, an LED, an RC LED or a
laser emitting multiple wavelengths, for example. It is understood
that the spectrum shown in FIG. 5 is provided for illustrative
purposes, and can look considerably different for different light
sources. The representative light source spectrum shown in FIG. 5
has a center wavelength given by .lamda..sub.center,Lightsource.
FIG. 6 shows the absorption spectrum of a sensing layer, such as
the sensor material shown in FIGS. 1-4. The representative
absorption spectrum shown in FIG. 6 has a center wavelength given
by .lamda..sub.center,Abs. FIG. 7 shows a representative light
source spectrum with a representative absorption spectrum of a
sensing layer. The center wavelengths of the two spectra are
labeled .lamda..sub.center,Lightsource and .lamda..sub.center,Abs,
respectively. For good performance, the illumination spectrum of
the light source should be chosen broader than the absorption
spectrum, so that the absorption spectrum can be positioned
non-centered within the illumination spectrum, as is shown in FIG.
7. Hence, the centroid of the input light spectrum is different
from the centroid of the illumination spectrum after interacting
with the sensing layer. In FIG. 7, three different absorption
levels of the sensing layer are shown respectively as broken lines
1, 2, and 3.
In accordance with various embodiments, it is important for the
functionality of the detection method that the absorption spectrum
of the sensing layer is placed non-centered within the illumination
spectrum of the input light source. In some embodiments, the
absorption spectrum can be predominantly incorporated into `one
half` of the illumination spectrum (e.g., the left side or right
side relative to the center wavelength). In the illustrative
embodiment of FIG. 7, it can be seen that the absorption spectrum
of the sensing layer is predominantly incorporated into the left
half of the illumination spectrum of the light source.
It is noted that the steeper the illumination spectrum is relative
to the width of the absorption spectrum, the more sensitive the
detection scheme will be with respect to changes in the absorption
characteristics. However, in general, the sensing layer should only
change the centroid of the illuminating light source with different
analyte concentrations. Thus, the absorption spectrum could also be
implemented such that it affects both sides of the illumination
spectrum, as long as the centroid of the illuminating light source
is altered by the sensing layer, rather than being incorporated
into one side of the illumination spectrum. It is further noted
that the FWHM of the absorption band can also be as broad as or
even broader than the FWHM of the illumination light. In this case,
the two bands should be off-centered far enough so that the
absorption spectrum effectively eats away one half of the
illumination spectrum. However, this configuration is less
preferred since it lowers the sensitivity of the sensing system. In
this case, only a portion of the absorption band of the sensing
layer overlaps with the incoming light and alters its spectral
distribution.
In some embodiments, rather than using a broad band illumination
source, a laser emitting multiple emission wavelengths (e.g.,
special multi wavelengths (or broad band laser) diode) or a
combination of laser diodes can be used. In such embodiments, a
portion of the emission wavelengths are affected by the absorption
band of the sensing layer, while another portion is not affected.
This relative change in the intensity of the emission wavelengths
can be measured with one wavelength centroid detector measuring the
spectral shift of the centroid of the emission lines.
As previously discussed, the interaction of the light source with
the sensing layer should be determined using a wavelength centroid
detector which measures the centroid of the spectral input light
distribution. There are many interrogation approaches that can be
used for this purpose. Particularly suited for this purpose is a
wavelength shift detection methodology that effectively converts
the task of measuring the wavelength of the incoming light to
measuring precisely the position of a light spot on a
position-sensitive detector. The wavelength information is encoded
into position information via a detector comprising a lateral
varying coating. One useful detector, for example, is a compact and
fast wavelength monitor that can resolve sub-pm wavelength
changes.
According to some embodiments, and with reference to FIG. 8, there
is shown a detector 802 that includes a position sensing device 806
and a filter 804 (e.g., linear variable filter) that cooperate to
convert the wavelength information of the incident light into a
spatial intensity distribution on the position sensing device 806.
Differential read-out of two adjacent elements 808 and 810 of the
position sensing device 806 is used to determine the centroid of
this distribution. A wavelength change of the incident light is
detected as a shift of the centroid of the distribution. The
detector 802 serves as a wavelength monitor, which can be used as a
readout unit for any optical sensor that produces a wavelength
shift in response to a stimulus.
With further reference to FIG. 8, the wavelength information of the
altered input light is converted via the filter 804 into spatial
information. Different filter approaches can be used, for example
bandpass filters with slightly different characteristics or a
linear variable filter as previously discussed. A linear variable
filter 804 transmits light of a certain wavelength only at a
certain position, and therefore acts as a position-dependent
bandpass filter. As an example, for the linear variable filter 804
shown in FIG. 8, shorter wavelengths get transmitted on the left
side, while longer wavelengths get transmitted at the right side.
The transmitted light is detected by the position sensing device
806, such as a photodiode (PD), which can be split in the middle
according to some embodiments, a so-called split diode. The two
separated regions 808 and 810 of the split diode of position
sensing device 806 can be called region I and region II, which are
also shown in FIG. 8. One half of the wavelength spectrum
transmitted through the filter 804 is detected by region I of the
position sensing device 806, whereas the other half of the
wavelength spectrum is detected by region II of the position
sensing device 806.
Thus, from the resulting photocurrents of the photo detector
regions 808 and 810 (which is proportional to the absorbed
photons), the centroid of the light distribution in the wavelength
regime can be determined, such as by taking the difference of the
photocurrents from detection region I and II and dividing this
difference by the sum of the photocurrents. By comparing the
photocurrent produced by the adjacent detector elements 808, 810, a
measure for the actual position of the centroid of the transmitted
light is obtained. In order to make the read-out signal stable
against intensity fluctuations, the signal can be normalized by the
total incoming intensity and is typically called Differential
Signal (S_Diff), which can be expressed as:
.times..times..times..times..times..times..about. ##EQU00001##
FIGS. 9 and 10 show a readout apparatus in accordance with various
embodiments. In the embodiments illustrated in FIGS. 9 and 10, the
sensing layer of the apparatus 1002 has an absorption spectrum
which is incorporated completely into one half of the illuminating
spectrum of the light source to provide for increased sensitivity.
The apparatus 1002 includes a wavelength-dependent filter 1004
(e.g., a linear variable filter or LVF) which is designed so that
its full spectral range just incorporates the illumination
spectrum, as is shown in FIGS. 9 and 10 (see the dashed outer lines
extending between FIGS. 9 and 10). Hence, the center wavelength of
the filter 1004 is the same as the center wavelength of the light
source. A position sensing device 1006, according to some
embodiments, includes a photodiode (PD), which can be implemented
as a split photodiode (regions I and II) centered to the filter
1004. Two representative cases are highlighted in FIG. 9 (see
curves 1 and 2) for purposes of illustration. It is noted that,
depending on the transducing mechanism, the light source spectrum
does not necessarily have to be changed in the described manner.
For example, the absorption can increase with analyte concentration
instead of decreasing behavior here or fluorescence can occur, for
example.
In the context of FIGS. 9 and 10, the light source spectrum is
altered by the absorption characteristics of the sensing layer,
which may also be referred to a transducing material. The
illuminating light source can be characterized by a certain FWHM
and a center wavelength .lamda..sub.center,Lightsource. The
absorption characteristic of the sensing layer can be described by
a certain FWHM and a center wavelength .lamda..sub.center,Abs. As
previously discussed, the filter 1004 can be a linear variable
filter (LVF) and the photodiode (PD) of the position sensing device
1006 can be a split-diode with photodiode sections I and II. The
detection ranges for the two photodiode sections I and II are also
marked in the spectrum plot on the wavelength axis (x axis), as
indicated by the dashed lines extending from the position sensing
device 1006 of FIG. 10 to the wavelength axis of FIG. 9. Two
different situations with different analyte concentrations are
shown in spectra 1 and 2 shown in FIG. 9. In situation 1, no
analyte is present; hence the absorption dip is largest and the
centroid of the light source spectrum lies on the right side
(labeled as .lamda..sub.C1). If the analyte concentration
increases, the absorption dip decreases, as is indicated by
spectrum 2. Hence, the centroid of the light distribution on the
position sensing device 1006 shifts to the left, as is indicated by
a different centroid wavelength .lamda..sub.C2, in this case. This
shift of the centroid leads to a change in the photocurrent in
regions I and II, and therefore changes the position sensing device
output signal S_Diff, as described above. It is noted that the
shift in centroid of the wavelength is exaggerated in FIG. 9 for
better visualization. In a real application, the shift might be
smaller. However the position sensing device 1006 described above
is highly sensitive even to the slightest changes of the
centroid.
Example 1
No Analyte Present
When no analyte is present, maximal absorption around the
absorption center wavelength .lamda..sub.center,Abs occurs. The
position sensing device 1006 determines the centroid of the
spectral distribution by comparing the intensities on both
photodiode sections I and II to each other. As significant
absorption takes place in the left side of the spectrum (photodiode
I), more photons get transmitted in section II (and therefore
larger photocurrent gets produced in section II) and hence the
centroid of the altered light source spectrum lies somewhere right
of the light source center wavelength
.lamda..sub.center,Lightsource and can be called
.lamda..sub.C1.
Example 2
Analyte Present
When an analyte specific to the sensing layer is present,
absorption of the sensing layer is decreased and the absorption dip
decreases slightly. In comparison to Example 1 above, more photons
now get transmitted onto photodiode I and the centroid of the
altered light source spectrum .lamda..sub.C2 shifts to the left,
yet still remains in the right section of the light source
spectrum.
FIG. 11 shows another embodiment of a sensing scheme, where the
wavelength centroid detector uses only a certain portion of the
light source spectrum for determining changes to the centroid of
the altered light source spectrum. If the detector design is
tailored to the absorption band of the sensing layer, the linear
variable filter transmission spectrum can be designed to be a bit
broader than the absorption band of the sensor, as is indicated in
FIG. 11 by the two sensing sections of the split diode labeled
again as regions I and II, respectively. In FIG. 11, the
characteristic absorption dip is visible with its center wavelength
.lamda..sub.enter,Abs. Curve 1 represents a situation where no
sensing agent is present. Curve 2 represents a situation where
sensing agent is present. The wavelength range of the linear
variable filter is indicated by the two detection regions of the
split diode marked by regions I and II, respectively. The detection
regions I and II are sensitive to the areas below curves 1 and 2,
respectively, which are labeled A.sub.11, A.sub.12, A.sub.21, and
A.sub.22.
In a situation where no sensing agent is present, a dip created by
the absorption of the sensing layer can be observed in the
transmission spectrum, shown in FIG. 11 and labeled as curve 1. The
voltage signal of detecting region I is proportional to the area
A.sub.11 below curve 1, while the voltage signal of detection
region II is proportional to the area A.sub.12 below curve 1.
Hence, the centroid of the light intensity can be
measured/determined accurately using the photocurrent signals
generated in detection regions I and II.
If the absorption coating of the sensing material is affected by a
sensing agent, the absorption coating will change its absorption
characteristics. This situation is depicted in FIG. 11 as curve 2.
In particular, with increasing concentration of the sensing agent,
the absorption dip will become smaller, as can be seen by comparing
curve 2 and curve 1 in FIG. 11. The photocurrent generated in
detection region I is still proportional to the left area under
curve 2, now called A.sub.21. In the same manner, the photocurrent
signal in detection region II is still proportional to the right
area under curve 2, now called A.sub.21. As can be seen in FIG. 11,
due to the monotonically rising/falling illumination spectrum, the
normalized changes in area between A.sub.11 to A.sub.21 and
A.sub.12 to A.sub.22 are not the same. Expressed
mathematically,
.noteq. ##EQU00002##
FIG. 12 illustrates the sensing characteristic, labeled curve 1,
and representative output signals S_Diff_1 and S_Diff_2 of a
wavelength centroid detector according to the centroid wavelengths
.lamda..sub.C1 and .lamda..sub.C2. Due to the detector
characteristic shown in FIG. 12, indicated by curve 1, a change in
the centroid in the wavelength .lamda..sub.C domain (e.g., from
.lamda..sub.C1 to .lamda..sub.C2) results in a change in the
detector output signal S_Diff. Thus, it is possible to detect a
change in the sensor signal when the absorption of the sensing
material changes and hence it is possible to read out the intensity
encoded sensor using the disclosed sensing principle with high
accuracy.
A sensor apparatus according to various embodiments can include a
light source, an analyte-sensitive coating (sensing layer), a
linear variable filter, and a photodiode implemented or deposited
together on the same substrate. In some embodiments, the
analyte-sensitive coating can be deployed on top of an light
source, such as an LED, RC LED or laser chip with multiple emission
wavelengths. A wavelength centroid detector is situated at the
other end of the optical path. Alternatively, the sensing layer can
also be placed somewhere between the light source and the detector
or directly deposited onto the wavelength centroid detector. It is
understood that many different configurations for the integration
of the readout apparatus can be chosen. For example, embodiments
using face-to-face integration via flip-chip mounting or in-plane
integration can be realized. Some embodiments may have optical
components added in the optical path in order to increase the
interaction of the light with the sensing layer or/and to increase
the light collection on the wavelength centroid detector. Also,
various deposition techniques can be used to grow a light source
and a detection unit next to each other on the same chip or
substrate.
FIG. 13 is a cross-sectional view of an integrated sensor structure
in accordance with various embodiments. The integrated sensor
structure includes an external stimulus or analyte-sensitive layer
1320 deposited onto an LED structure 1301. The LED structure 1301
includes a substrate 1304 (e.g., n.sup.+ substrate), an epitaxial
layer 1306 (n.sup.+/p layers), insulator/oxide 1308, and a contact
layer 1310. Light generated by the LED structure 1301 passes
through the sensing layer 1320 and is received by a wavelength
centroid detector 1350. The wavelength centroid detector 1350
measures any analyte induced changes of the emitted LED spectrum,
and can be placed at the other side of an analyte chamber according
to some embodiments. In FIG. 13, the representative wavelength
centroid detector 1350 includes a split diode photodetector 1356
covered with a linear variable filter 1354. In some embodiments,
the sensing layer 1320 can be deposited onto the wavelength
centroid detector 1350. In some embodiments, the sensor structure
shown in FIG. 13 can be integrated into a dense sensing enclosure
as an integrated unit.
Various embodiments provide for a high degree of integration and
scalability that reduces response time of the entire sensing
apparatus. The use of high integration fabrication techniques makes
it easy to implement large arrays of sensors which allows for
increasing the detection reliability (e.g., redundant sensor
pixels), the realization of multiplexed sensors (different pixels
are sensitive to different analytes) or for increasing the dynamic
range of the sensor (e.g., by choosing an array of sensors
sensitive for the same analyte but sensitive to different ranges of
concentration). By using different analyte-specific coatings for
each pixel, for example, the sensor can provide for multiplexed
analyte detection (see e.g., FIGS. 14, 15, 18). A large variety of
coatings can lead to very specific detection even if each
individual sensing layer is only "weakly" specific. This is
typically achieved by employing certain evaluation techniques like
principal components analysis, which searches for a characteristic
detection pattern.
FIG. 14 shows a detection apparatus 1400 comprising an array of
light sources 1402 (LS1-LSN), an array of wavelength detectors 1404
(D1-DN), and an array of sensing layers 1408 of varying types
positioned therebetween. The array of sensing layers 1408 comprises
a multiplicity of sensing layers whose optical properties change in
response to the presence of a specific external stimulus. For
example, array of sensing layers 1408 may comprise a multiplicity
of analyte-specific sensing layers (e.g., analyte-specific coatings
ASC1-ASCN), each of which is sensitive to a different analyte. In
the embodiments illustrated in FIG. 14, the light sources 1402 can
be of various types (e.g., LED, RC LED, OLED, etc.) On the other
side of the optical path, an array of wavelength detectors 1404
(which are capable of measuring the centroid of the incoming light
distribution) with analyte-specific coatings 1408 is directly
deposited on top of the wavelength detectors 1404 according to some
embodiments. For analyte-specific detection, different coatings
1408 can be applied on each detector 1404 in order to provide
specific detection on each detector 1404 for component analysis,
for example. In order to increase the light sensitivity, optical
components can be added between the light sources 1402 (e.g., an
LED array or one or more large area LEDs facing the detector array
1404) in order to improve the photon flux.
If the wavelength centroid detector array 1404 is made sensitive to
a specific wavelength band, natural illumination (e.g., sunlight or
spectrally filtered sunlight to match the incoming light to the
absorption spectrum of the sensing layer) may be used, and
detection can involve measuring the analyte-induced changes
referenced to a wavelength detector sensitive to the same
wavelength band but not covered with an analyte specific sensing
layer. This referencing might be needed if e.g., natural sun light
is used as input light which can spectrally change during
measurement. The representative examples discussed above involve
intensity changes caused by an analyte-induced absorption change in
a sensing layer.
It is understood that other intensity changes can be used to sense
for the presence of a specified external stimulus, such as a
specific analyte. For example, analyte-induced changes in the
fluorescence intensity can be employed to create changes in the
centroid of the spectral distribution of light impinging on the
wavelength detector (see FIG. 16). Especially sensitive are
embodiments were the centroid of the input light is subject to
alteration by both absorption and fluorescence emissions. In FIG.
16, the light source spectrum with analyte-induced absorption dip
is labeled `1`, and the analyte-induced change in the fluorescence
intensity is labeled `2`. Both influences change the centroid of
the altered light source spectrum.
FIG. 15 shows a detection apparatus 1500 comprising an array of
light sources 1502 (LS1-LSN), an array of phosphors 1506 (P1-PN) of
differing types, an array of detectors 1504 (D1-DN), and an array
of sensing layers 1508 of varying types positioned therebetween.
The array of sensing layers 1508 comprises a multiplicity of
sensing layers whose optical properties (e.g., absorption and
fluorescence) change in response to the presence of a specific
external stimulus. For example, the array of sensing layers 1508
may comprises a multiplicity of analyte-specific sensing layers
(e.g., analyte-specific coatings ASC1-ASCN), each of which is
sensitive to a different analyte. Each of the sensing layers of the
array 1508 requires illumination with a specified spectral range
provided by an appropriate phosphor (a selected one of P1-PN) of
the array 1506. Illuminating each sensing layer of the array 1508
using an appropriate phosphor of the array 1506 converts the
emission spectrum of the light source 1502 to the required
wavelength spectrum for each sensing layer.
In the embodiments illustrated in FIG. 15, the light sources 1502
can be of various types (e.g., LED, RC LED, OLED, etc.) The array
1502 can also include laser light sources (e.g., blue or UV laser
diodes), since the phosphor array 1506 converts the laser light to
the appropriate broad band light source needed as input light for
the sensing layers 1508. The apparatus 1500 also includes an array
of wavelength centroid detectors 1504 with analyte-specific
coatings 1508 directly deposited on the detectors 1504 according to
some embodiments. For analyte-specific detection, different
coatings 1508 can be applied on each detector 1504 in order to
provide specific detection on each detector 1504 for principal
component analysis or specific pattern recognition, for example. As
discussed previously, in order to increase the light sensitivity,
optical components can be added between the light sources 1502
(e.g., an LED array or one or more large area LEDs facing the
detector array 1504) in order to improve the photon flux.
The various examples discussed above use transmission geometry for
sensing. However, many sensing concepts also work in reflection.
For example, a fiber sensor with an analyte-specific coating can be
used in reflection by placing a mirror at the end facet of the
fiber (two pass transmission). Such as fiber sensor may be more
sensitive per fiber length since the light interacts twice with the
sensing material (one time on its way to the end facet of the fiber
and one time on the way back from the end facet). In a free space
embodiment, for example, the sensing layer can be deposited on a
mirror and the light source and wavelength detector can be arranged
under 45 degree. In order to increase the sensitivity of the
sensing system, the analyte-specific sensing layers can also be
placed in a cavity between the input light and the wavelength
centroid detector in order to increase the interaction length
between input light and sensing layer.
FIG. 17 illustrates another embodiment of a sensing apparatus 1700
comprising an array of wavelength centroid detectors 1704, an array
of phosphors 1706, and an array of sensing layers 1708 positioned
between the array of detectors 1704 and the array of phosphors
1706. In the embodiment shown in FIG. 17, analyte-induced changes
in absorption and fluorescence emissions can be used to detect the
presence of specific analytes. The magnitude of the detected
changes in centroid of the light spectrum can also be measured to
determine the concentration of the specific analytes.
In the embodiment illustrated in FIG. 17, the detection apparatus
1700 includes a single light source 1702, which can be of various
types (e.g., GaN LED or LD or SiC LED). In some embodiments, optics
1703 (e.g., one or more lenses) are positioned between the light
source 1702 and the array of phosphors 1706. The optics 1703 direct
input light produced by the light source 1702 to each cell of the
phosphors array 1706 and to corresponding sensing layers 1708 and
detectors 1704. In other embodiments, an array of light sources can
be used, such as those shown in FIGS. 14 and 15, in which case the
optics 1703 need not be included. In some embodiments, each
phosphor in the array of phosphors 1706 can be shaped to act like a
lens arranged to direct light from the light source 1702 towards
the sensing layers 1708 and detectors 1705.
The light source 1702 (or array of light sources) and lenses 1703
(if present) are arranged to ensure that light emitted from the
light source 1702 gets focused on the correct sensing layer 1708
and wavelength centroid detector 1704. Each sensing layer of the
array 1708 which requires illuminations with different spectral
ranges can be correctly illuminated by choosing the appropriate
phosphor of the array 1706 in order to convert the emission
spectrum of the light source 1702. In some embodiments, the light
source 1702 can include an array of LEDs covered with phosphors
1706 providing the required wavelength spectrum for the
analyte-specific sensing layers 1708. Such embodiments provide for
a larger variety of sensing layers 1708 that can be combined on the
same chip, even if the sensing layers 1708 are working in different
spectral ranges. In some embodiments, the entire phosphor array
1706 can be supported by the same LED type. The functionalization
of the different sensors (e.g., deposition of phosphors and sensing
layers) can be accomplished with printing, for example.
Each of the analyte-specific sensing layers 1708 has an associated
phosphor 1706. Each of the analyte-specific sensing layers 1708 has
an absorption and fluorescence spectrum that is non-centered with
respect to an illumination spectrum of the light source 1702. The
presence of a specific analyte causes a change in absorption and
fluorescence emissions of a particular analyte-specific sensing
layer 1708 which can be sensed by its associated wavelength
centroid detector 1704. In some embodiments, the wavelength
centroid detectors of the array 1704 have analyte-specific coatings
1708 deposited directly on the detectors 1704 (e.g., to form an
integrated structure). For analyte-specific detection, different
coatings 1708 can be applied on each detector 1704 in order to
provide specific detection on each detector 1704 for component
analysis, for example. According to the embodiment of FIG. 17,
analyte-induced changes in absorption and the fluorescence
intensity for each sensing layer of the array of sensing layers
1708 can be employed to create changes in the centroid of the
spectral distribution of light impinging on each detector of the
array of wavelength centroid detectors 1704. Especially sensitive
are configurations where the centroid of the light is altered by
both absorption and fluorescence emissions.
FIG. 18 is a block diagram of a sensing apparatus 1802 in
accordance with various embodiments. The apparatus 1802 includes a
light source 1806 which produces input light that is coupled into
an optical wave guide 1810. The optical wave guide 1810 includes a
sensing layer 1812 or an array of sensing layers 1812, each of
which comprises an analyte-specific material whose optical
properties change in the presence of a specific analyte or
stimulus. The sensing layer 1812 is arranged on the optical wave
guide 1810 to interact with the input light and to asymmetrically
alter a spectral distribution of the input light in response to
presence of a specific analyte. The altered input light is coupled
from the optical wave guide 1810 to a wavelength centroid detector
1815.
According to some embodiments, the detector 1815 includes a linear
variable filter 1822 optically coupled to a photodetector 1824. The
detector 1815 determines a shift in the centroid of the altered
input light relative to a centroid of the spectral distribution of
the input light in response to presence of the specific analyte.
The detector 1815 can also be configured to determine a magnitude
of the shift in the centroid of the altered input light (e.g., the
concentration of the specific analyte or magnitude of the
stimulus).
The photodetector 1824 is implemented as a position-dependent photo
detection device according to various embodiments. In some
configurations, for example, the photodetector 1824 is implemented
as a split diode photodetector of a type previously described.
Using the resulting photocurrents of the photodetector's split
sections (e.g., regions I and II), the centroid of the light
distribution in the wavelength regime can be determined by
circuitry 1828 of the detector 1815. The circuitry 1828, for
example, can be configured to measure the difference of the
photocurrents from detection region I and II of the photodetector
1824 and divide this difference by the sum of the photocurrents,
thereby providing a signal that comprises information about the
actual position of the centroid of the transmitted light. In order
to make the read-out signal stable against intensity fluctuations,
this signal can be normalized by the circuitry 1828 using the total
incoming intensity (e.g., the differential signal S_Diff, discussed
previously). The detector 1815 may include an optional separator
component 1820 configured to collimate and/or spread the light from
the optical wave guide 1810 across an input surface of the linear
variable filter 1822.
The detection apparatus 1802 may include or be coupled to an
optional processor 1832 and/or a display 1830. The processor 1830
may be part of a larger system, such as an analyzer for example,
and can cooperate with the detector 1815 to provide enhanced
features and functionality. For example, the processor 1830 may be
configured to communicatively couple to the detector 1815 for a
variety of purposes, including data collection, updating
programmable components of the detector 1815 (e.g., circuitry
1828), calibrating the detector 1815, and communicatively linking
the detector 1815 to other devices and interfaces (e.g., an
Internet interface). The optional display 1830 may be coupled
directly to the detector circuitry 1828 (e.g., an input/output
interface) or indirectly via the processor 1832. Data recorded by
the detector 1815 can be presented on the display 1830, such as
textual and graphical data.
Various embodiments of the disclosure provide for highly accurate
detection of a specific analyte(s) at a relatively low cost. Some
embodiments, for example, need only include one low cost light
source (e.g., an LED) and one inexpensive sensor for readout. As
previously discussed, sensing in another wavelength regime for
compensation of source fluctuations is not required within this
scheme, hence the detection scheme can be made more compact and
cheaper than comparable readouts. In some embodiments, for example,
the sensor used for readout is insensitive to intensity
fluctuations of the incident light source and additional unwanted
intensity fluctuations introduced on the optical path to the
detector. Embodiments of the disclosure effectively convert an
intensity-encoded sensor into a wavelength-encoded sensor with its
inherent advantages.
Embodiments of the disclosed wavelength detection technique have
been shown to be extremely sensitive to wavelength shifts of the
centroid even for light with a relatively broad FWHM (e.g., LED).
Embodiments of a readout scheme disclosed herein have been shown to
be highly suitable for tracking the intensity changes within even
rather broad absorption bands. Embodiments of the disclosed
detection scheme have been found to be compatible with existing
sensing materials and sensing apparatuses. For example, a readout
scheme of the present disclosure can replace an existing detection
schemes while keeping the sensor itself. A readout scheme of the
present disclosure is suitable for a broad range of detection bands
and adjustable also in the width of the absorption peak to be
detected and tracked.
Systems, devices, or methods disclosed herein may include one or
more of the features, structures, methods, or combinations thereof
described herein. For example, a device or method may be
implemented to include one or more of the features and/or processes
described herein. It is intended that such device or method need
not include all of the features and/or processes described herein,
but may be implemented to include selected features and/or
processes that provide useful structures and/or functionality.
In the above detailed description, numeric values and ranges are
provided for various aspects of the implementations described.
These values and ranges are to be treated as examples only, and are
not intended to limit the scope of the claims. For example,
embodiments described in this disclosure can be practiced
throughout the disclosed numerical ranges. In addition, a number of
materials are identified as suitable for various implementations.
These materials are to be treated as exemplary, and are not
intended to limit the scope of the claims.
The foregoing description of various embodiments has been presented
for the purposes of illustration and description and not
limitation. The embodiments disclosed are not intended to be
exhaustive or to limit the possible implementations to the
embodiments disclosed. Many modifications and variations are
possible in light of the above teaching.
* * * * *